In SMN1-related proximal spinal muscular atrophy (SMA), the intravenous treatment Zolgensma is indicated for infants and young children weighing less than 21 kg with type I SMA or carrying a biallelic mutation of the SMN1 gene and a maximum of 3 copies of the SMN2 gene. According to the Phase III STEER and STRENGTH trials, the same gene therapy, this time administered intrathecally and called Itvisma, is effective in patients aged 2 to 18 years.
The multicentre STEER trial included 126 treatment-naïve patients aged 2 to 18 years who were able to sit but not walk independently.
- Seventy-five received gene therapy and 51 received a sham procedure.
- During one year of follow-up, motor function, the primary endpoint assessed using the HFMSE score, was significantly improved in treated patients compared to the control group.
- The greater improvement in the HFMSE score in the gene therapy group was observed as early as the fourth week of follow-up.
- This mode of administration was also well tolerated.
The STRENGTH multicentre trial involved 27 patients aged 2 to 18 years who had previously received treatment with Spinraza (nusinersen) or Evrysdi (risdiplam).
- All patients received Itvisma.
- The safety profile of gene therapy (primary endpoint) was consistent with that observed in treatment-naive patients.
- Motor function, assessed as a secondary endpoint using the HFMSE score, was stable during the one-year follow-up period.
Itvisma gene therapy has been approved in the United States for patients over 2 years of age since December, while in Europe, the application for approval is pending.
